Magnetrons



1961 M. ESTERSON E'l'AL 2,972,084

MAGNETRONS Filed July 51, 1958 F16. PRIOR ART \NVNTOR-Si ca. 621M faaua W UM United States Patent G MAGNETRONS Maurice Esterson and Francis James Weaver, Essex, England, assignors to English Electric Valve Company Limited, London, England, a company of Great Britain Filed July 31, 1958, Ser. No. 752,277 Claims priority, application Great Britain Mar. 31, 1958 2 Claims. (Cl. 31539.53)

This invention relates to multi-cavity resonator magnetrons and more particularly to power output arrangements therefor.

' The invention is illustrated in and explained in connection with the accompanying drawings in which Fig. 1 is a simplified sectional view of a known multi-cavity resonator magnetron and power output' arrangement therefor, Fig. 2 is a similar View illustrating this invention, and Fig. 3 is a section on the line III-III of Fig. 2. In both Figs. 1 and 2 the magnetron is only schematically represented, being shown broken away at the end remote from the power output arrangement.

'It is well known to obtain improved performance and output from a multi-cavity resonator magnetron by using a so-called symmetrical output power arrangement which is such as not to disturb the symmetry of the radio frequency field distribution which occurs around the anode system when oscillation is taking place in the customary 1r mode. Fig. 1 illustrates a known arrangement of this nature.

In Fig. 1 the rnulti-cavity anode block is represented at 1 and power output is taken off by means of a co-axial line having its axis on the axis of the anode system. The inner member comprises a tapered portion 2 which tapers down from a large diameter near the anode block to a smaller diameter parallel sides portion 3, the far end of which is used as a coupling probe to feed energy into a rectangularly sectioned main output guide 8. The configuration of the co-axial line outer conductor accords approximately with that of the inner conductor and consists of two cylindrical portions 4 joined by a tapered portion 5. The end of the inner conductor 2 adjacent the anode block is connected to alternate anode segments by connectors 6. So as not to complicate the drawing only two such connectors are shown in Fig. 1 though actually there is one to each of the alternate anode segments. The end of the outer conductor of the line adjacent the block 1 is sealed in a vacuum tight manner thereto and the other end of said outer conductor is closed ofi in a vacuum tight manner by a dielectric window 7 which is shown as domed. Thus the outer conductor of the line forms part of the vacuum tight envelope of the magnetron. The main output guide has in one wall thereof a circular aperture to which a short cylindrical member 9 leads. In use the unit comprising themagnetron with its attached coaxial line is inserted as shown into the cylindrical member 9 so that the end of the portion 3 acts as a probe coupling with the main guide 8 and launching a H wave therein. The length of the co-axial line is indicated by the dimension L and the intrusion of the probe into the main guide is indicated by the dimension J. The arrow headed lines represent directions of the electric field vector.

This known arrangement, like other similar known arrangements in which output is taken from a magnetron by a co-axial line which is used to feed energy to a probe or the like to launch a H wave down a main output guide, has a number of serious electrical and structural defects which are due in the main to the fact that the end ice of the line which is attached to the anode system is a high impedance point (i.e. the voltage there is high and the current is low). Since the lead into which the magnetron has to work is, in normal practice, of relatively low impedance, some impedance transformation is necessary if satisfactory coupling is to be obtained. It is possible to achieve the required impedance transformation in the coaxial line and use a matched transition from the said line to the waveguide. In practice, however, if this is done the ratio of co-axial line inner diameters has to be of such value as to make the whole arrangement structur-ally most inconvenient if not actually impracticable. It is therefore much simpler and practical to mis-imatch the transition between the co-axial line and the main output waveguide to obtain the required coupling, but here again there is the defect that if this is done the intrusion of the probe end of the co-axial line into the guide (i.e. the dimension 1) has to be very small and is, moreover, so critical in value that the obtaining of correct coupling in this way is difiicult both to achieve in manufacture and to maintain after manufacture. Furthermore, an appreciable proportion of the radio frequency energy is stored in the co-axial line so that small changes in dimensions or small departures in manufacture from intended dimensions are apt to cause the frequency of magnetron oscillation to depart unacceptably from the required frequency.

The present invention seeks to overcome the abovementioned defects and to provide an improved power output system which is relatively simple to construct, does not impose close limits or tolerances of dimension, and which is capable of handling high powers.

According to this invention a symmetrical power output arrangement for a multi-cavity resonator magnetron includes a disc mounted coaxially of the anode system and connected to alternate anodes by connectors mounted within and parallel to one end of the anode block, a length of circularly sectioned waveguide co-axially encircling said disc and having one end attached to the anode block, and a dielectric window across the other end of said length of guide, the whole arrangement being such that when the magnetron is operating in the 11' mode, the coupling member launches an E wave into said length of guide.

The coupling member may be a ring or a disc. A disc, however, is preferred since its solid center assists in protecting the dielectric Window from possible bombardment by charged particles.

The dielectric window may be a disc or it may be domed.

It will be seen that an arrangement in accordance with this invention constitutes a mechanical unit which can be readily mounted to feed output power into a rectangularly sectioned main output waveguide by providing the latter with a matched circular transition in one wall of said main guide and having its axis at right angles to the main guide axis, and inserting the window end of said unit coaxially into the open end of said transition. If this is done an H wave will be projected down the main guide and, by suitably dimensioning the parts in accordance with known principles, efficient output coupling from the magnetron and a good degree of impedance matching can be obtained in a practical manner.

Fig. 2 illustrates the present invention. In Fig. 2, reference character 1 again designates the anode block and 8 the rectangularly sectioned main output guide. There is, however, no co-axial line for feeding output to the main guide. Instead there is a coupling disc which is mounted parallel to and a short distance from one end of the anode block and is connected to alternate anode segments by conductors 6 running parallel to the axis and, in the case illustrated, serving also as mechanical supports for the coupling disc 10. For the same reason as in Pig.

3 1, only two such conductors are shown in Fig. 2. The disc 10 is concentrically within a cylindrical length of guide 11 which is brazed in a vacuum-tight manner to the anode block at one end and is sealed off at the other by a dielectric window so that it forms part of the evacuated envelope of the magnetron. The dielectric window may take any of a variety of forms, for example, it may be a simple disc as represented at 7a or a domed window as represented at 7b. These two forms of windows are drawn in broken lines in Fig. 2 to indicate that they are alternative forms. The end of the guide length 11 remote from the magnetron is inserted in a cylindrical transition.

member 12 opening into the main guide. In use, when the magnetron is oscillating in the 1r mode, the coupling disc 10 launches an E wave into the cylindrical guide section 11, the wave passing then through a matched transition section and entering the main guide 8 down which an H wave is projected. The arrow headed lines again represent electric field vectors, the lines Ebeing appropriate to the E wave, and the lines H being appropriate to the H wave. The coupling disc 10 acts as the impedance'transformer so that the circular-to-rectangular guide transition can be matched and there is practically no energy storage in the circular section. The extent of coupling is controlled by the diameter of the disc and the lengths of the connectors 6, i.e. the distance of the disc from the adjacent end of the anode block. Dimensional tolerances are very much less close with an arrangement as shown in Fig. 2 than with a known arrangement as shown in Fig. 1, the improvement as respects the most critical dimension being about ten times.

Another advantage of the arrangement of Fig. 2 over that of Fig. l is that the dielectric window is in a matched guide so that, for a given transmitted power, the electric field intensity is lower than it would otherwise be. Ac-

4 cordingly improved power handling capacity is obtained, since the dielectric window provides in practice a limitation of the power that can be handled.

Furthermore, the disc 10 protects the dielectric window from charged particles which might otherwise be accelerated along the axis of the magnetron from the anodecathode interaction space thereof.

We claim:

1. A magnetron and symmetrical power output arrangement for launching an axially symmetrical waveguide mode comprising a multi-cavity resonator magnetron, the vacuum-tight envelope of which includes a length of circularly sectioned waveguide closed at one end by a dielectric window and attached at the other to one end of the magnetron anode block, a disc mounted coaxially both with said guide length and the anode system of the magnetron and connected to alternate anodes of the magnetron by connectors mounted within said guide length adjacent and parallel to said one end of the anode block, an output waveguide and a transition waveguide member arranged between said length of circularly sectioned waveguide and said output waveguide.

2. A magnetron and output arrangement as claimed in claim 2 wherein the output guide is of rectangular section and the transition member of circular section, the latter extending at right angles to said output guide and leading to the interior thereof through one wall thereof, and

wherein the said length of waveguide is coaxial with and has its window end inserted in the open end of said transition member.

References Cited in the file of this patent UNITED STATES PATENTS 

